The present invention relates to a magnetic tape recording and reproducing apparatus, and more particularly to a magnetic tape recording and reproducing apparatus of the helical scan type for recording signals on and reproducing signals from a magnetic tape wound helically around a rotatable head drum having a head while the head is scanning the magnetic tape slightly obliquely with respect thereto.
Magnetic tape recording and reproducing apparatus of the helical scan type operate in a signal recording mode by rotating a head on a head drum slightly obliquely with respect to the longitudinal direction of a magnetic tape as it is fed along in a forward direction at a certain speed. As shown in FIG. 1 of the accompanying drawings, such helical scanning produces a video track 2 on a magnetic tape 1 at an angle .theta. with respect to the longitudinal direction of the magnetic tape 1. When the recorded signal is reproduced in a normal-speed mode, the scanning path of the rotating head coincides with the video track 2, and the signal can be reproduced properly without noise. However, when the recorded signal is reproduced in a so-called fast-forward mode while the tape 1 is running in the direction of the arrow X.sub.1, the rotating head scans the tape 1 along a path 3 deviated from the video track 2. Similarly, when the signal reproduction is carried out in a fast-reverse mode during the travel of the tape 1 in the direction of the arrow X.sub.2, the rotating head scans the tape 1 along a path 4 also deviated from the video track 2. The scanning paths 3, 4 are inclined at angles .theta..sub.1 (&gt;.theta.) and .theta..sub.2 (&lt;.theta.), respectively, with respect to the longitudinal direction of the tape 1. The rotating head thus scans the tape 1 across plural tracks 2, resulting in a tracking error which produces noise on the reproduced image. FIG. 1 shows the angles as being exaggerated, and the difference between the angle .theta. and the angle .theta..sub.1 or .theta..sub.2 is actually on the order of a fraction of degree.
Different attempts have been made to eliminate the noise caused by the tracking error in the high-speed playback modes. One such attempt has employed a piezoelectric device such as a bimorph cell as an attachment for a rotating head, the bimorph cell being curved upon application of a control voltage thereto for bringing the scanning path of the rotating head into conformity with the video track on the tape. According to another effort, tape guides for guiding the magnetic tape in positions located upstream and downstream of the head drum in the direction of travel of the tape are vertically displaced to change the lead angle of the tape with respect to the drum, so that the video track on the tape will be aligned with the scanning path of the rotating head.
The former arrangement has suffered problems in that the piezoelectric device is difficult to control and is expensive. The latter proposal has been disadavntagous since the vertical displacement of the running tape causes a tracking error at an audio control head. Another drawback is that one longitudinal edge of the tape is pushed against and folded by a flange of the tape guide near the capstan, reulting in a curled tape.